1. Field of the Invention
This invention pertains to apparatus suitable for paving large slab areas, particularly on bridge spans, and a method of paving such areas.
2. Description of the Prior Art
Equipment employed for constructing concrete roads have become increasingly more automated so as to minimize the need for making such construction efforts heavily labor-intensive. As a result, dirt excavation, hauling and placement equipment has been developed for road construction purposes which is highly automatic. With respect to concrete paving equipment used on roads, where once the tasks were almost exclusively done by hand, such equipment is now available to uniformly distribute the poured concrete, grade the pavement to close tolerances and to finish or surface large areas in accordance with rigid design specifications.
Even much of bridge construction is automated or at least prefabricated with the wide-spread use of concrete forms developed to the point where complete bridge bents or span segments are put into place and then set and adjusted with a few bolts and jacks. However, although roadway pavement on the ground has been successfully converted to the use of automated or semi-automated equipment, when the same tasks are performed on a bridge, after the forms and reinforcing steel are in place, the work is still highly labor intensive.
The construction equipment industry has developed and has for many years marketed equipment to perform uniform distribution, achieve close tolerance grading and effect suitable surface finishing of roadway pavement on bridges; however, its use has been limited for lack of a practical and stable means of supporting such equipment where it can be used over the full area where slabs are to be poured. In addition, there has been no practical and economical means of support and supplying or transporting the concrete slurry from a source located in proximity to the other equipment.
There have been two general approaches used in the prior art with limited success for pouring concrete in position on a bridge. In the first approach, the rails on which the equipment are to run are set on the outside edge forms of the deck slab, which is, in turn, are supported on overhand brackets hung from the outside of the bridge beam. This procedure allows the equipment to reach most of the surface area, but because the geometry of the brackets is unstable, especially under the heavy loads imposed by concrete distribution equipment, only light finishing equipment can be used in this approach. The heavy work of uniform distribution of the concrete must be left to be done manually.
The key to why the brackets are unstable can be better understood by a more detailed understanding of their construction. The brackets are attached by a single bolt to an internal hanger that is anchored to the bridge beam, in a manner that provides easy erection and permits the easy removal of the bracket after the concrete has been placed and cured. The internal hanger remains imbedded in the concrete. This construction allows the hanging of the bracket manually from the top of the beam without the use of scaffolding. All the currently popular brackets employ this construction.
Because the overhang bracket is by its nature a cantilever, a combination of imposed vertical loads and reaction horizontal loads must be provided for. The currently popular brackets provide for this combination of vertical and horizontal loads by hanging the bracket from the "hanger" with the single bolt placed at a 45 degree angle between the vertical and horizontal, in anticipation that the two loads will balance each other. In normal usage where the brackets carry only the concrete deck, the two loads do balance close enough to provide satisfactory results. However, when loading varies from equipment wheel loads well out on the brackets to concrete loads nearer the supporting beam the two loads do not balance and the bolt must swing from its 45 degree angle to an angle that will coincide with the imbalance of the loads. This swinging of the hanger bolt obviously causes the bracket, forms and equipment rail to move from their set positions in a rocking motion under loads alternating between moving equipment loads and concrete loads. Some contracting agencies will not permit even the use of light finishing equipment carried on the currently popular overhang brackets because their unstable geometry gives mixed results, as to uniformity and consistency of the grade.
In the second approach, the concrete and forms are carried on overhang brackets, but rails on which the equipment spread is to run is supported on "chairs" above the finished grade over two outside bridge beams. This technique provides for efficient use of the paving equipment spread, including uniform distribution, close tolerance grading, and finishing of most of the area between the two outside bridge beams, but leaves the area within a couple of feet and to the outside of the beams to be worked by hand. Moreover, the rails and their supporting "chairs" must be immediately removed and the "chair holes" patched and refinished. Tine texturing must be done by hand.
The method disclosed and claimed herein is specifically designed to support both concrete distribution and finishing equipment on rails mounted outside of the paved area so the entire area can be worked, and to do so with stability so that the grades established before concrete placement starts will be there after placement is finished.
To overcome the problem of instability under moving loads while maintaining all the convenience of a single bolt attachment to an internal hanger, the beam member of a preferred bracket used in the procedure to be described is designed with a rigid vertical beam extension on the attachment end of the beam. This bracket construction is more completely described and shown in detail in U.S. Pat. No. 4,660,800 entitled "Bridge Overhang Bracket and Hanger", issued Apr. 28, 1987, Eugene A. Horstketter, which application is incorporated herein for all purposes. Since the top of this vertical extension will be encased in the concrete along with the hanger, but will be withdrawn as the bracket is removed, it is preferably made conical to assure ease of removal. The hanger bolt extends through the top of the cone and attaches to the hanger. As the nut on the bolt is tightened, it draws the top of the cone up into a recess in the hanger, resulting in an attachment that permits limited swival action, but which will not permit either vertical or horizontal movement of the beam end regardless of the balance between imposed vertical loads and reaction horizontal loads due to concrete placement or moving equipment.